How voters use political issues to elect political candidates is of central importance to our understanding of democratic representation. Research on voting behavior often assumes that American voters hold distinct economic and cultural issue preferences. In this research note, we point out that this does not necessarily imply that preferences for candidates’ positions on the two issue dimensions are also additively separable in voters’ decisions. Analyzing survey data on US presidential elections from 1996 to 2016, we estimate to what extent voters’ economic and socio-cultural preferences are nonseparable and find that the two general dimensions act as substitutes in their decisions. Our finding implies that voting decisions are partially structured by an underlying single dimension, as liberal deviations from a voter’s ideal point on social issues can be compensated by conservative deviations on economic issues.